1. Field of the Invention
The present invention relates to a control valve for controlling the discharging capacity of a variable displacement compressor.
2. Description of the Related Art
An automotive air conditioner is generally configured by arranging and placing a compressor, a condenser, an expander, an evaporator, and so forth in a refrigeration cycle. The compressor is, for example, a variable displacement compressor (hereinafter also referred to simply as a “compressor”) capable of varying the refrigerant discharging capacity in order to maintain a constant level of cooling capacity irrespective of the engine speed. In this compressor, a piston for compression is linked to a wobble plate, which is mounted to a rotational shaft driven by an engine. The angle of the wobble plate is changed to change the stroke of the piston, by which the refrigerant discharging rate is regulated. The angle of the wobble plate is changed continuously by supplying part of the discharged refrigerant into a hermetically-closed control chamber and thus changing the balance of pressures working on both faces of the piston. The pressure (referred to as a “control pressure” below) Pc in this control chamber is controlled by, for example, a control valve provided between a discharge chamber and the control chamber of the compressor.
One example of such a control valve includes a main valve provided in a main passage through which a discharge chamber and a control chamber communicate with each other, and a sub-valve provided in a sub-passage through which the control chamber and a suction chamber communicate with each other, both of which are driven by a single solenoid (refer to Japanese Unexamined Patent Application Publication No. 2014-95463, for example). With this control valve, during steady operation of the air conditioner, the opening degree of the main valve is controlled in a state where the sub-valve is closed. This enables control of the control pressure Pc as mentioned above, so as to control the discharging capacity of the compressor. In contrast, at the startup of the conditioner, the sub-valve is opened in a state where the main valve is closed. This enables a so-called bleeding function of rapidly lowering the control pressure Pc so that the compressor can relatively quickly enter a maximum capacity operation state.
Related Art List
(1) Japanese Unexamined Patent Application Publication No. 2014-95463.
In such a control valve, however, power supply to the solenoid is typically controlled using the pulse width modulation (PWM) technique. Thus, vibration caused by the PWM control may cause the sub-valve to open, as will be described later. For example, if the main valve element hits the main valve seat when the main valve is slightly open, the impact may cause the sub-valve to open, which may substantially affect the control of the main valve.